The invention relates to a method for accelerating a vehicle having an electric motor as a drive and an internal combustion engine as a drive, in other words for accelerating a hybrid vehicle. The invention also relates to such hybrid vehicle.
In particular, when accelerating a hybrid vehicle from a standstill, it makes sense to initially carry out the acceleration with assistance from the electric motor, because the electric motor is capable of producing a high torque at low rotation speeds. A changeover to the drive with the internal combustion engine is advantageous at higher rotation speeds.
However, the internal combustion engine has frequently previously been turned off, for example in a start-stop operation following a complete stop of the vehicle. If it is desired to turn the internal combustion engine on after the acceleration by the electric motor has begun, the internal combustion engine must first be tow-started to be started. A separate electric motor can be used for tow-starting; but this case is not of interest here. Presently, the situation is considered where the electric motor operates not only as a drive, but is also used for tow-starting the engine.
If it is desired to also tow-start the engine with the accelerating electric motor in the midst of a driving phase with acceleration, a certain torque to be provided by the electric motor must be kept in reserve for tow-starting. In other words, only a partial torque of an available torque of the electric motor is used for acceleration, so that the difference between the available torque and the partial torque can then be subsequently used to tow-start the engine; otherwise, jerking would be produced while transitioning to tow-starting the engine due to the reduction of the driving torque; such jerking should be prevented.
From some vehicles, e.g. from sports cars, the so-called launch control is known. The vehicle can hereby be placed into a mode where it reaches a certain speed as fast as possible when accelerating from a standstill, for example as fast as possible from 0 to 100 km/hr. Sports vehicles have, for example, actuators which can be used to briefly switch this mode on, for example when starting at a traffic light. Such mode is not known for hybrid vehicles.
DE 10 2007 055 828 A1 describes a method for operating a hybrid vehicle wherein the internal combustion engine can be started in various modes from an electric drive mode. A tow-start, a rope start and an engine start with interrupted pulling-force are described as engine start variants. A start mode is selected here in response to a start request by using an evaluation of predetermined selection criteria depending on the current operating situation.
DE 10 2006 045 824 A1 describes a method for controlling a hybrid drive vehicle, in which various driving modes are provided, which relate to a boost behavior in a defined operating situation. Here, a mode can be selected by the driver via a manually operable sports switch.
DE 10 2009 027 642 A1 describes a method for operating a hybrid vehicle, wherein the hybrid vehicle starts up electrically at a first startup, wherein the internal combustion engine is started before, during or after the startup and is operated in a separated combustion operating mode for heating the catalytic converter. Furthermore, the internal combustion engine is prevented from contributing to the propulsion as long as the catalytic converter has not heated up.